An agricultural combine is a machine used to harvest a variety of crops from a field. When corn is to be harvested, the combine is equipped with a corn head assembly or “corn head” at the front of the machine. The corn head includes a series of row dividers that guide corn stalks into respective row units as the combine advances over the corn stalks. The corn stalks are guided in each row unit to ear separation chambers or stripping plates which strip the ears of corn from the stalks. Some corn heads feature chopping mechanisms or “choppers” with rotating blades for cutting and shredding the stalks after the ears are stripped from the stalks. The ears are then conveyed rearwardly to a trough containing an auger. The auger conveys the ears to a feederhouse that feeds the ears into the combine. The ears are then threshed, cleaned and temporarily stored in a grain tank for temporary holding.
Row units are often driven by a drive shaft that extends through all of the row units in a direction transverse to a forward direction of movement of the combine. Choppers are also driven by a drive shaft, which may be the same drive shaft that drives the row units, or a different drive shaft. It is not uncommon for a row unit or chopper to become jammed with crop material during operation, preventing the row unit or chopper from operating. In such a case, the slip clutch that connects the drive shaft to the jammed row unit or chopper disengages to protect the drive shaft and upstream components from overload. The slipped clutch allows the drive shaft to continue rotating, but no more power is delivered to the jammed row unit or chopper.
If a slipped clutch is not detected and addressed in time, the clutch can become damaged beyond repair. In addition, the combine may continue to operate in a partially disabled condition. Unfortunately, slip clutches are concealed in the corn head and not visible to the operator during operation of the combine. Therefore, the operator cannot always see when a clutch is slipping from their vantage point inside the driving cab.
When a clutch slips, the rotational speed of the row unit drive shaft or chopper drive shaft changes. Therefore, one option for detecting a slipped clutch is to install speed sensors to monitor the speed of each row unit and chopper. This approach is not practical, however, because it requires the installation of a speed sensor at each row unit and each chopper, which can be expensive to install and maintain.
U.S. Pat. No. 7,739,861 describes a system that detects clutch slippage using a vibration sensor based on vibration frequency. A single vibration sensor can be placed in the corn head to detect vibration frequencies associated with a slipped clutch. The vibration sensor measures vibration frequency and conveys the measurements to a band pass filter by way of an analog to digital converter. Band passed frequencies are examined by a comparator to determine if the frequencies exceed a certain threshold. If the band passed frequencies exceed the threshold, an audio or visual indication is provided to alert the operator of a slipping clutch.
One of the drawbacks of frequency-based vibration analysis is that the system requires many components, sensors and inputs to work properly. As pointed out in U.S. Pat. No. 7,739,861, there are many sources of vibrations in a corn head frame during a harvesting operation. Unless extraneous vibrations are eliminated, the extraneous vibrations (or “noise”) prevent the processing unit from determining when a slip clutch is slipping. For this reason, systems that utilize frequency-based vibration analysis include an adjustable band pass filter. The pass band of the filter is centered about a “predominant frequency” representative of vibration frequencies that are produced when a monitored clutch slips. The vibration frequency produced by a slipped clutch is a product of the rotational speed of the drive shaft and the number of teeth in the clutch. Drive shaft speed is not constant, of course, but can be adjusted by the operator to accommodate different operating conditions. As a result, the vibration frequency caused by a slipping clutch is not a constant, but varies depending on the speed of the drive shaft. The predominant frequency for the pass band filter must therefore adapt to changing rotational speeds of the drive shaft. For this reason, frequency-based systems require a speed sensor on the drive shaft to continually measure drive shaft rotation and adjust the band pass so that only frequencies associated with slipping clutches are passed. In addition, information about the type of slip clutch (e.g. number of teeth) must be input into the controller to calculate the predominant frequency. Consequently, frequency-based vibration monitoring systems require many more components, sensors and data inputs to function, and involve constant processing of data by the controller.
There remains a need for a more streamlined, efficient, reliable and cost-effective system for detecting a clutch slippage in a combine harvester, and for alerting an operator of the slippage.